1. Field of the Invention
The invention is concerned with apparatus and systems in which light or other radiant energy is modified as, for example, by switching. Contemplated systems include communications, computers, etc.
2. Description of the Prior Art
A significant part of modern technology is concerned with apparatus and systems in which radiant energy is in some way altered during transmission through a medium. Communication systems, for example, may make use of a carrier wavelength of radiation energy which is somehow altered in analog or digital manner so as to represent intelligence. An increasing part of technology depends upon computer systems of increasing sophistication which, again, generally depend upon variation of some characteristic of energy-electromagnetic energy--with complex computations being the cumulative result of a multiplicity of such variations, possibly in discrete control elements. Both types of systems have, in the past, depended on relatively low frequency energy, perhaps dc, while later developments make increasing use of higher and higher frequency energy. This trend has gained impetus through the invention and development of the laser oscillator, variations of which may now produce cw or pulsed radiation at wavelengths from the far infrared through the visible spectrum and into the ultraviolet.
Many of the now realized implications of the laser oscillator were recognized at its inception. These include increased bandwidth and rapidity of both introduction and extraction of information. Exploitation necessarily suggest a variety of circuit elements--some operating as shutters, some as switches, some as digital modulators, etc. Control elements suggested in response to this recognized need have operated on virtually every physical principle known. These include magnetooptic interactions, such as Faraday rotation and induced birefringence effects; electrooptic effects, including--e.g., Kerr effect or Pockel's effect. Elements may constitute pulse generating means, some internal to the laser, itself, as by Q-switching, mode-locking, cavity dumping; and some external to the laser, for example, by use of saturable absorbers. A variety of devices depend as well upon acoustooptic effects. Dependence upon a variation in index of refraction due to a travelling or stationary elastic wave may, for example, result in physical displacement of energy to fill a number of operational needs.
An observed phenomenon which received considerable scientific acclaim, known as induced transparency, is described in Physical Review Letters, 18, 908 (1967) by S. L. McCall and E. L. Hahn. The effect, experimentally observed as self-induced coherent amplification, may take the form of transmission of a pulse of radiant energy through an excited medium, resulting, first in an initial absorption thereby reducing pulse length, with subsequent stimulation resulting in amplification of the now shortened pulse.